When did VW start inserting plastic baffles inside the valve covers of 1.6D engines ??
I now on the gas engines it happened as soon as the heads went hydraulic lifter to keep down some of the oil spray from the "new" oil squirter pointed at the cam. Prolly the same with the diesels.
Moved to General. Not IDI engine / power enhancement related.
I'm guessing 86 since my 85 Jetta didn't have one but my 86 did.